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Wafers
Determine whether there is a difference between probes in measuring resistance. Blood Pressure 2
Determine whether four drugs differ in mean increase in systolic blood pressure. |
Wafers: Problem |
The National Institute of Standards and Technology (NIST) references research involving the doping of silicon wafers with phosphorus. The wafers were doped with phosphorus by neutron transmutation doping in order to have resistivities of 200 ohm/cm. Measurements of bulk resistivity of silicon wafers were made with 5 probing instruments on each of 5 days. The experimenters are interested in testing differences among the instruments.
Complete an ANOVA to determine whether there is a difference between the probes in measuring resistance. If there are differences, then distinguish them by using a test for multiple comparisons. |
Lee Creighton (modified by Paris Faison)
SAS Institute
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Wafers: Sample Data | |
The Doped_wafers data set gives the resistance measurements for 5 different probing instruments from a study conducted by the National Institute of Standards and Technology. These are the variables in the data set: Name | Type | Description | | Instrument | num | probing instrument (categorical) | | Resistance | num | resistance measurement | |
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Source of Data
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Sall, J., Creighton, L., & Lehman, A. (2006). JMP Start Statistics, Third Edition. Cary, NC: SAS Institute Inc. |
Wafers: Solution |
The value of the F statistic for the ANOVA F test is 1.18 with a corresponding p-value of 0.3494, which is not significant. So, the data does not indicate that there is a difference between the probes in measuring resistance. This is supported by the results from the Tukey test for multiple comparisons. These results were generated by performing the analysis in SAS Enterprise Guide.
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Blood Pressure 2: Problem |
Suppose that a pharmaceutical company has recently focused on the effect of its potential products on blood pressure. Researchers conducted a study in which the subjects were 72 individuals with one of three diseases. Eighteen individuals were randomly assigned to each of the four drugs. The treatments were administered over time and the increase in systolic blood pressure was recorded. Perform a one-way ANOVA to determine whether there are significant differences between the mean increases in systolic blood pressure for the four drugs. If there are, you need to determine which drugs differ and how greatly they differ. |
SAS Institute Inc.
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Blood Pressure 2: Sample Data | |
The Drug data set contains data from an experiment to evaluate the effect of four different drugs on blood pressure for individuals with one of three possible diseases. These are the variables in the data set: Name | Type | Description | | Drug | char | drug (1, 2, 3, 4) | | Disease | char | disease (A, B, C) | | BPChange | char | change in systolic blood pressure | |
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Source of Data
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This data is sample data from SAS Institute Inc. |
Blood Pressure 2: Solution |
The p-value of .0001 is less than .05, so there is sufficient evidence to reject the null hypothesis that all means are equal. The F test does not give any specifics about which means are different, only that there is at least one pair of means that is statistically different. To compare means, you can use a test such as Tukey's studentized range test (HSD). For example, in the results for Tukey's test, drugs 1 and 2 are significantly different from 3 and 4. |
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